"Using a Mac may certainly be a safer choice for a lot of people as despite being vulnerable they are not targeted. However this is not the same as Macs being secure, something Eric Schmidt erroneously advised recently. I may be able to browse impervious to malware on a Mac at the moment, however I personally would not be comfortable using a platform so easily compromised if someone had the motivation to do so. In this article I address just why OS X is so insecure including the technical shortcomings of OS X as well as Apples policies as a company that contribute to the situation."

Ah. Another Mac fanboy who either doesn't want to admit it was a worm, or doesn't know what the definition of a worm is. Leap.A took advantage of a JPEG decoder vulnerability in iChat as others pointed out. And propegated by sending itself to other people in your iChat contact list. So yes, by definition, it was a worm.

This exploit toolkit was a low threat-level multiplatform exploit tool that allows it to take advantage of poor upgrade implementations by injecting fake updates. (not a worm or virus)

It was a worm because one of the fake updates that it was possible to inject through it was the exploit tool itself, which would then turn the infected Mac into a fake update server that could infect other Macs. Again, it meets the definition of a worm.

This is the only example where you have a point and even this worm had flaws that made it highly unlikely to be seen in the wild.

It was seen in the wild. But as I said, not very often because Macs were not very common in the wild. It mostly infected corporate networks that had a lot of Macs running on them.